The present invention relates generally to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device capable of forming an silicon-on-insulator (SOI) structure only in a desired region.
In the semiconductor industry, trends in the development of semiconductor devices are leading to devices having high integration, high speed operation and low power consumption Realizing a desired operation within a decreased area is necessary to achieve these semiconductor devices. A capacitorless memory device has recently been mentioned as having promise in the semiconductor industry. A capacitorless memory device can store and read out data by charging up a plurality of carriers in a floating body and changing the threshold voltage of a cell.
A typical capacitorless memory device is realized using an SOI substrate, which has a stack structure of a silicon substrate, a buried oxide layer and a silicon layer. Advantages of capacitorless memory devices include: the ability to accomplish high speed operation by a small junction capacitance that is less than that of a typical dynamic random access memory (DRAM), voltage reduction as a result of a low threshold voltage, and prevention of a latch-up phenomenon as a result of complete isolation.
However, although the capacitorless memory device realized on the SOI substrate has the above-described advantages, side effects, such as a floating body effect, are likely to be caused.
In detail, in a capacitorless memory device realized on an SOI substrate, electron holes continuously accumulate in the low potential area of the body of a floating transistor, that is, the lower portion of the boundary area between a source region and a channel region. When the electron holes accumulate in this manner, the potential of the channel increases, the threshold voltage decreases, and the drain voltage-current characteristics of the transistor change as observed in a kink effect.
Additionally, depending upon the use of the semiconductor device, there may be one case in which it is advantageous to realize the semiconductor device on an SOI device even though a floating body effect is caused, and then another case in which the floating body effect causes problems.